Investigations of rabbit T lymphocytes have involved the use of monoclonal antibodies and cDNA probes to follow gene expression under normal and pathologic conditions. DNA probes for these studies were obtained from a cDNA library prepared using RNA from a rabbit cell line transformed with the virus Herpes ateles. Probes are now available for constant and variable region T cell receptor alpha and beta chain genes and for class I T cell specific products. In addition, class II genes homologous to HLA-DR, -DQ, -DP, and -DZ have been cloned from rabbit libraries. In addition, probes for the human genes CD4 and CD8 have been obtained and are being tested for use in our studies of T cell subpopulations. These studies involve determination of the normal pattern of gene expression in resting rabbit lymphocytes and in lymphocytes stimulated with T cell mitogenic agents. In addition, a model for crescentic glomerulonephritis that is induced by formation of immune complexes is also under study in collaboration with investigators from the University of Michigan. It was shown that T cells infiltrate the glomerulus and after several days become positive for MHC class II genes and synthesize increased amounts of T cell receptor beta chains. These studies have used antibodies directed against the class II antigens and markers for T cells and have been verified by Northern blot analyses of control and diseased kidneys.